In a given metropolitan area, a particular communication user may have theoretical access to a plurality of RF communication systems. The basic operation and structure of commonly available communication systems, such as dispatch communications systems and cellular communications systems are known.
Dispatch communication systems typically comprise a dispatch application processor (DAP), a limited number of repeaters that transceive information via communication channels, and a plurality of mobile subscriber (MS) units which may be mobile vehicle radios and/or portable radios. Of the communications channels, one is typically chosen to be a control channel. The control channel typically transceives operational information between the DAP and the MS units, such that, for example, the MS units can access the communications channels. Dispatch systems efficiently support group dispatch (group calls) which allows multiple MS units to simultaneously access one communication channel. Private or individual telephone calls are also possible.
Cellular communication systems typically comprise a mobile telephone switching office, also known as a message switching center (MSC), a plurality of cells, a limited number of communication channels, and a plurality of MS units which may be cellular telephones. Each of the plurality of cells comprises some of the limited number of communication channels, wherein one of the communications channels is designated as the control channel for that cell. The control channel transceives operational information between the plurality of communication units within the cell and the MSC such that communication units can place telephone calls via a phone system such as the Public Switched Telephone Network (PSTN).
As a result of recent advances in technology, users or subscribers can now use one communication unit to transceive in either system and to further receive or transceive messages from yet other network entities. In a geographic region, for example, that contains both a dispatch communications system and a cellular communications system, wherein the two network entities have substantially overlapping coverage areas and are operably coupled to one another, a user can operate in either system. Note is made that such network entities may, but need not, share the same RF resources, i.e., share a base transceiver link.
Presently, interworking communication systems, i.e., communication systems that are in fact overlays of multiple systems, give subscribers (within specific geographic regions) access to a variety of services, including interconnect call and circuit data call services processed by the MSC, private call and group call services processed by the DAP, and short message services (paging) processed by a network entity known as a short message service switching center (SMS-SC), the latter which may be coupled directly to the MSC. In the future, it is envisioned that other communication network entities, capable of providing, for example, packet data communications. (via RF links to remote MS units, such as computers and the like) could also be interconnected.
Unfortunately, most of the services presently offered by each network entity do not interwork from a mobile termination viewpoint. Whichever service receives a channel to the MS unit first is the service that the subscriber gets. Consequently, if some other service type attempts to connect to the active MS unit it will not be able to. For example, when a subscriber is currently involved in an interconnect call, a call from the dispatch system (group call or private call) will not be able to connect, interrupt or alert the subscriber of the incoming call. This problem is known in the industry as the `bifurcation problem`. Many subscribers would like the option of choosing whether to continue in the current service (e.g., an MSC-processed call), or to end or to put on hold the current call to connect to the incoming call from a different service (e.g., a DAP-processed call), but are currently unable to do so.
At present, both the DAP and the MSC maintain what is known as a busy list. The busy list concept allows a subscriber to assign priority levels and/or incoming-call options with regard to the particular call types serviced by an associated network entity. However, there does not exist a means which allows a subscriber to define which of plural services is to have priority over a current call, when the service of the current call is different from that of the incoming call and provided by a different network entity.